Power tool

ABSTRACT

A first recess and protrusion engagement portion and a second recess and protrusion engagement portion making a fan guide and one end portion of a leg swingably abut on each other and making a base plate and the other end portion of the leg swingably abut on each other, respectively, and restricting a deviation of the leg relative to the fan guide and the base plate in a horizontal direction while allowing swinging of the leg relative to the fan guide and the base are provided between the fan guide and the one end portion and between the base plate and the other end portion, respectively. The leg can swing with almost no resistance without involving any elastic deformation during the orbital motion of the base, and stress to cause elastic deformation is not applied to the leg unlike the conventional art.

CROSS-REFERENCE TO RELATED APPLICATION

The present application claims priority from Japanese Patent ApplicationNo. 2012-074260 filed on Mar. 28, 2012, the content of which is herebyincorporated by reference into this application.

TECHNICAL FIELD OF THE INVENTION

The present invention relates to a power tool which is provided with amain body part having a driving source, a rotation shaft provided in thedriving source, and a base moving in an approximately circular motion ina horizontal direction with respect to the main body part along withrotation of the rotation shaft, and performs grinding work using apolishing sheet held by the base.

BACKGROUND OF THE INVENTION

Conventionally, power tools are used to efficiently grind and smoothen asurface of a wood or the like, and the power tools include a so-calledorbital sander provided with a main body part having a driving source, arotation shaft provided in the driving source, and a base moving in anapproximately circular motion in a horizontal direction with respect tothe main body part along with rotation of the rotation shaft (making anorbital motion). Also, the base is designed to hold a polishing paper(polishing sheet). Therefore, when a user grasps a grip of the main bodypart to rotationally drive the driving source and presses the polishingpaper onto a surface of a wood or the like, the base makes an orbitalmotion with respect to the main body part to efficiently grind andsmoothen the surface of the wood or the like.

As such an orbital sander (power tool), for example, an electric powertool described in Japanese Patent Application Laid-Open Publication No.2008-100302 (Patent Document 1) has been known. In the electric powertool (power tool) described in Patent Document 1, a motor (drivingsource) is housed in a housing (main body part) and a ball bearing isprovided at a distal end portion of a motor shaft (rotation shaft) ofthe motor so as to be eccentric to an axial center of the motor shaft.Further, a base provided with a pad which holds a polishing paper isfixed to the ball bearing, and a plurality of flexible legs (posts) areprovided between the housing and the base and around the ball bearing.These legs restrict relative rotation of the base with respect to thehousing and also allow swinging action of the base relative to thehousing centered around the ball bearing, so that the base (polishingpaper) makes an orbital motion along with rotation of the motor shaft.

SUMMARY OF THE INVENTION

According to the power tool described in Patent Document 1 mentionedabove, however, since one ends of the respective posts are fixed to themain body part and the other ends thereof are fixed to the base, eachtime when the base makes an orbital motion with respect to the main bodypart, namely, each time when the power tool is used, the respectiveposts repeat elastic deformation such as extension and contraction.Therefore, when the respective posts deteriorate due to a long-term useof the power tool, cracks occur in the respective posts in some cases,which results in the necessity of maintenance such as replacement. Inparticular, in the case where the power tool is frequently used in asite where an ambient temperature is low, not only the deterioration ofthe respective posts is accelerated to shorten a maintenance cycle butalso the respective posts are hardened to make the elastic deformationdifficult. As a result, an operation resistance of the base isincreased, which may result in such a problem that the grindingperformance lowers.

An object of the present invention is to provide a power tool capable ofpreventing the increase in the operation resistance of the base andextending the maintenance cycle of the posts.

According to one embodiment, a power tool includes: a main body parthaving a driving source; a rotation shaft provided in the drivingsource; a base moving in an approximately circular motion with respectto the main body part in a horizontal direction along with rotation ofthe rotation shaft; a polishing sheet held by the base; a post providedbetween the main body part and the base; and recess and protrusionengagement portions provided between the main body part and one endportion of the post and between the base and the other end portion ofthe post, respectively, making the main body part and the one endportion swingably abut on each other and making the base and the otherend portion swingably abut on each other, respectively, and restrictinga deviation of the post relative to the main body part and the base in ahorizontal direction while allowing swinging of the post relative to themain body part and the base.

According to the present invention, the post is swung with almost noresistance without involving any elastic deformation during the orbitalmotion of the base. Therefore, stress (load) to elastically deform thepost like the conventional art is not applied to the post, and theincrease in the operation resistance of the base can be prevented andthe life of the posts can be prolonged to extend the maintenance cycle.

BRIEF DESCRIPTIONS OF THE DRAWINGS

FIG. 1 is a perspective view showing an orbital sander according to afirst embodiment of the present invention;

FIG. 2 is a partial sectional view of the orbital sander taken along alongitudinal direction of the orbital sander as viewed from the side ofarrow A in FIG. 1;

FIG. 3 is a partial sectional view showing a portion B circled by abroken line in FIG. 2 in an enlarged fashion;

FIG. 4A is an operation explanatory diagram for describing an operationstate of a leg;

FIG. 4B is an operation explanatory diagram for describing the operationstate of the leg;

FIG. 5 is a partial sectional view showing a leg and a surroundingstructure thereof according to a second embodiment and corresponding toFIG. 3;

FIG. 6 is a partial sectional view showing a leg and a surroundingstructure thereof according to a third embodiment and corresponding toFIG. 3; and

FIG. 7 is a partial sectional view showing a leg and a surroundingstructure thereof according to a fourth embodiment and corresponding toFIG. 3.

DESCRIPTIONS OF THE PREFERRED EMBODIMENTS

A first embodiment of the present invention will be described below indetail with reference to the drawings.

FIG. 1 is a perspective view showing an orbital sander according to thefirst embodiment of the present invention, FIG. 2 is a partial sectionalview of the orbital sander taken along a longitudinal direction of theorbital sander as viewed from the side of arrow A in FIG. 1, FIG. 3 is apartial sectional view showing a portion B circled by a broken line inFIG. 2 in an enlarged fashion, and FIGS. 4A and 4B are operationexplanatory diagrams for describing an operation state of a leg.

As shown in FIG. 1 and FIG. 2, an orbital sander 10 as a power tool isprovided with a sander main body 20 and a base 30. The sander main body20 is provided with a housing 21 which can be divided into a left sideportion and a right side portion (a far side portion and a near sideportion in FIG. 1) along a longitudinal direction of the orbital sander10, and the housing 21 is formed from a resin material such as plasticso as to have a hollow shape.

The housing 21 is provided with a motor housing portion 21 a and a gripportion 21 b. A motor 22 serving as a driving source in an uprightposition is housed inside the motor housing portion 21 a and anoperation switch 11 for turning ON and OFF the orbital sander 10 isprovided on the grip portion 21 b. A stopper button 12 (see FIG. 1) isprovided in the vicinity of the operation switch 11 on the grip portion21 b. Then, by pressing the stopper button 12 in a state where theoperation switch 11 has been operated to ON, the continuous operationstate where the operation switch 11 is not operated to OFF is achieved.

Here, for easy understanding of an internal structure of the housing 21,illustrations of electric wires for electrically connecting theoperation switch 11 and the motor 22, a power source cord 13, apolishing paper 14, clips 15 (see FIG. 1), and the like are omitted inFIG. 2.

A fan guide 23 formed in a predetermined shape from a resin materialsuch as plastic is provided in the housing 21 near the base 30. The fanguide 23 is fixed inside the housing 21, and a rotation shaft 22 aextending in a downward direction below the motor 22 penetrates throughan approximately central portion of the fan guide 23. The rotation shaft22 a of the motor 22 is rotatably supported by a first radial bearing B1attached to the fan guide 23, and a cooling fan 24 is fixed to a distalend side of the rotation shaft 22 a below the first radial bearing B1 inan axial direction so as to be rotated integrally with the rotationshaft 22 a. Here, the sander main body 20 is composed of the housing 21and the fan guide 23, and the housing 21 and the fan guide 23 constitutea main body part in the present invention.

The cooling fan 24 is rotatably housed inside the fan guide 23 via adust guide 25, and is provided with a dust collecting function tocollect grinding dusts (not shown) generated during the grinding work inaddition to a cooling function to cool the motor 22. A plurality ofcooling fins 24 a are provided on the motor 22 side of the cooling fan24, and a plurality of dust collecting fins 24 b are provided on thebase 30 side of the cooling fan 24 so as to face an exhaust port 25 a ofthe dust guide 25. Therefore, external air can be fed to the motor 22along with the rotation of the cooling fan 24, and grinding dusts can befed to the inside of a dust collecting bag 26 (see FIG. 1) via theexhaust port 25 a. Here, the dust collecting bag 26 is formed of, forexample, a cloth with a mesh size allowing the air to pass but notallowing the dusts to pass.

An eccentric piece 27 is fixed to a distal end side of the rotationshaft 22 a below the cooling fan 24 in the axial direction of therotation shaft 22 a via a fastening screw S. The eccentric piece 27 isdesigned to make an orbital motion (eccentric circular motion) around anaxial center C2 at a position decentered (offset) from an axial centerC1 of the rotation shaft 22 a by about 1.0 mm, and an inner side of asecond radial bearing B2 is attached to a piece main body 27 a formingthe eccentric piece 27. Further, a cylindrical portion 31d providedintegrally on a base plate 31 forming the base 30 is fixed to an outerside of the second radial bearing B2, so that the base 30 also makes anorbital motion via the second radial bearing B2 by the orbital motion ofthe eccentric piece 27 along with the rotation of the rotation shaft 22a. More specifically, the base 30 is designed to move in anapproximately circular motion in a horizontal direction with respect tothe housing 21 and the fan guide 23 along with the movement of theeccentric piece 27.

A weight 27 b is provided partially around the piece main body 27 a soas to cancel (balance out) vibrations in a horizontal direction causedby the orbital motion of the base 30. Specifically, as shown in FIG. 2,when the base 30 moves to the right side in FIG. 2, the weight 27 bmoves to the left side in FIG. 2. Thus, by cancelling the vibrations inthe horizontal direction during the operation of the orbital sander 10in this manner, the movement of the grip portion 21 b grasped by aworker in the horizontal direction can be prevented.

The base 30 is composed of the base plate 31 made of an aluminummaterial and a sponge-like pad 32 made of a rubber material, and apolishing paper 14 (see FIG. 1) serving as a polishing sheet is attachedto the pad 32. When the polishing paper 14 is to be attached to the pad32, both end portions of the polishing paper 14 in a longitudinaldirection of the orbital sander 10 are folded back to the side of thebase plate 31 and they are secured by clips 15 attached to the baseplate 31. Here, a hole is also formed in the polishing paper 14 so as tocoincide with dust collecting hole (not shown) formed in the base plate31 and the pad 32. Therefore, grinding dusts generated during thegrinding work are collected in the dust collecting bag 26 via the holeformed in the polishing paper 14, the dust collecting hole, and the dustguide 25 (exhaust port 25 a).

A total of four legs (posts) 40 are provided between the fan guide 23forming the sander main body 20 and the base plate 31 forming the base30. Though only two legs are shown in FIG. 2, the respective legs 40 areeach formed in an approximately columnar shape from an elastic materialsuch as rubber, and they are arranged at predetermined intervals atfront, back, left and right positions along the horizontal direction ofthe fan guide 23 and the base plate 31 so as to interpose the rotationshaft 22 a of the motor 22. Here, since the respective legs 40 andsurrounding structures thereof are all identical to one another, one leg40 and a surrounding structure thereof will be described in detail withreference to FIG. 3.

As shown in FIG. 3, a first recess and protrusion engagement portion(recess and protrusion engagement portion) 50 is provided between abase-side surface 23 a of the fan guide 23 and one end portion 40 a(upper side in FIG. 3) of the leg 40. The first recess and protrusionengagement portion 50 is composed of a columnar member 51 integrallyprovided so as to extend in the axial direction of the rotation shaft 22a from the base-side surface 23 a toward the base plate 31 and aspherical recess portion 52 formed so as to be recessed from the one endportion 40 a of the leg 40 toward the other end portion 40 b thereof. Aspherical protrusion portion 51 a is integrally provided at a distal endof the columnar member 51, and the spherical protrusion portion 51 aabuts on the spherical recess portion 52. Therefore, swinging of the leg40 relative to the fan guide 23 is allowed and axial deviation of theleg 40 relative to the fan guide 23, namely, relative movement(deviation) of the leg 40 with respect to the fan guide 23 in thehorizontal direction is restricted.

A radius R1 of the spherical protrusion portion 51 a is set to beslightly smaller than a radius R2 of the spherical recess portion 52(R1<R2). Therefore, a distal end of the spherical protrusion portion 51a is brought in point contact with a bottom of the spherical recessportion 52. By brining the spherical protrusion portion 51 a and thespherical recess portion 52 into point contact with each other in thismanner, the leg 40 can swing smoothly with almost no resistance duringthe orbital motion of the base 30. Here, a height of the columnar member51 including the spherical protrusion portion 51 a is set to be largerthan a depth of the spherical recess portion 52. In this manner, in theswinging action of the leg 40 relative to the fan guide 23, the contactbetween the one end portion 40 a of the leg 40 and the base-side surface23 a is prevented, so that the base 30 can make an orbital motionsmoothly.

An annular first surrounding wall 23 b is integrally provided around thecolumnar member 51 of the fan guide 23 so as to surround the columnarmember 51. The one end portion 40 a of the leg 40 in its longitudinaldirection is housed in the first surrounding wall 23 b in a non-contactstate, and a height of the first surrounding wall 23 b from thebase-side surface 23 a is set to h1. By setting the height of the firstsurrounding wall 23 a to h1 in this manner, about ⅓ of the leg 40 in thelongitudinal direction is covered with the first surrounding wall 23 b.As a result, even if the leg 40 is elastically deformed largely by anycause, the leg 40 is prevented from flying out of the first surroundingwall 23 b.

A taper surface 23 c gradually thinned toward a distal end (lower sidein FIG. 3) of the first surrounding wall 23 b is formed on a radiallyinner side of the first surrounding wall 23 b. An inclination angle ofthe taper surface 23 c is set to α°, and the inclination angle α° is setto be equal to the maximum inclination angle of the leg 40 when the leg40 swings. In this manner, _(t)he one end portion 40 a of the leg 40 iseasily housed in the first surrounding wall 23 b when assembling theorbital sander 10. Further, the contact between the leg 40 and the firstsurrounding wall 23 b during the swinging action of the leg 40 can beprevented, so that the base 30 can make an orbital motion smoothly (seeFIG. 4).

A second recess and protrusion engagement portion (recess and protrusionengagement portion) 60 is provided between a fan-guide-side surface 31 aof the base plate 31 and the other end portion 40 b (lower side in FIG.3) of the leg 40. The second recess and protrusion engagement portion 60is composed of a columnar member 61 integrally provided so as to extendin an axial direction of the rotation shaft 22 a from the fan-guide-sidesurface 31 a toward the fan guide 23 and a spherical recess portion 62formed so as to be recessed from the other end portion 40 b of the leg40 toward the one end portion 40 a thereof. A spherical protrusionportion 61 a is integrally provided at a distal end of the columnarmember 61, and the spherical protrusion portion 61 a abuts on thespherical recess portion 62. Therefore, swinging of the leg 40 relativeto the base plate 31 is allowed and axial deviation of the leg 40relative to the base plate 31, namely, relative movement (deviation) ofthe leg 40 with respect to the base plate 31 in the horizontal directionis restricted.

A radius R1 of the spherical protrusion portion 61 a is set to beslightly smaller than a radius R2 of the spherical recess portion 62(R1<R2). Therefore, a distal end of the spherical protrusion portion 61a and a bottom of the spherical recess portion 62 are brought into pointcontact with each other. By bringing the spherical protrusion portion 61a and the spherical recess portion 62 into point contact with each otherin this manner, the leg 40 can swing smoothly with almost no resistanceduring the orbital motion of the base 30. Here, a height of the columnarmember 61 including the spherical protrusion portion 61 a is set to belarger than a depth of the spherical recess portion 62. In this manner,in the swinging action of the leg 40 relative to the base plate 31, thecontact between the other end portion 40 b of the leg 40 and thefan-guide-side surface 31 a can be prevented, so that the base 30 canmake an orbital motion smoothly.

An annular second surrounding wall 31 b is integrally provided aroundthe columnar member 61 of the base plate 31 so as to surround thecolumnar member 61. The other end portion 40 b of the leg 40 in itslongitudinal direction is housed in the second surrounding wall 31 b ina non-contact state, and a height of the second surrounding wall 31 bfrom the fan-guide-side surface 31 a is set to h2 (h2<h1). By settingthe height of the second surrounding wall 31 b to h2 in this manner,about ¼ of the leg 40 in the longitudinal direction is covered with thesecond surrounding wall 31 b. As a result, even if the leg 40 iselastically deformed largely by any cause, the leg 40 is prevented fromflying out of the second surrounding wall 31 b.

Here, the height hi of the first surrounding wall 23 b and the height h2of the second surrounding wall 31 b can be arbitrarily set,respectively. For example, they may be set so as to have a magnituderelationship opposite to that described above. However, in setting theheights h1 and h2, it is desirable that a predetermined clearance (withthe size of about ¼ of the leg 40 in the longitudinal direction) isformed between the first surrounding wall 23 b and the secondsurrounding wall 31 b so as to absorb slight displacement of the base 30relative to the fan guide 23 in the operation of the orbital sander 10.

A taper surface 31 c gradually thinned toward a distal end (upper sidein FIG. 3) of the second surrounding wall 31 b is formed on a radiallyinner side of the second surrounding wall 31 b. An inclination angle ofthe taper surface 31 c is set to α°, and the inclination angle α° is setto be equal to the maximum inclination angle of the leg 40 when the leg40 swings. In this manner, the other end portion 40 b of the leg 40 iseasily housed in the second surrounding wall 31 b when assembling theorbital sander 10. Further, the contact between the leg 40 and thesecond surrounding wall 31 b during the swinging action of the leg 40can be prevented, so that the base 30 can make an orbital motionsmoothly (see FIG. 4).

Next, the action of the orbital sander 10 formed in the above-describedmanner, particularly, the swinging action of the leg 40 during theorbital motion of the base 30 will be described in detail with referenceto the drawings.

As shown in FIG. 2, first, when a worker grasps the grip portion 21 b ofthe orbital sander 10 and operates the operation switch 11 to turn ON inthis state, driving current is supplied to the motor 22. Then, therotation shaft 22 a is rotated about the axial center C1 and theeccentric piece 27 makes an orbital motion about the axial center C2along with the rotation. As a result, the base 30 (base plate 31) alsomakes an orbital motion via the second radial bearing B2, so that thepolishing paper 14 (see FIG. 1) attached to the pad 32 also makes anorbital motion. Thereafter, by pressing the polishing paper 14 onto asurface of a wood or the like, the pressed portion of the surface can beefficiently ground to be smoothened.

At this time, as shown by arrows SW1 and SW2 in FIGS. 4A and 4B, thebase 30 makes an orbital motion with respect to the fan guide 23, andthe leg 40 makes a swinging action so as to pivot on the columnarmembers 51 and 61 within the range of the maximum inclination angle α°(see FIG. 3) along with the orbital motion of the base 30. Here, sinceFIGS. 4A and 4B are planar views, they represent swinging actions onlyin the left and right directions (arrows SW1 and SW2) of the leg 40, butthe leg 40 actually swings also in a depth direction in FIGS. 4A and 4B.

In the swinging action of the leg 40, since the leg 40 is made ofrubber, is in point contact with the columnar member 51 made of plasticand the columnar member 61 made of aluminum, and is not elasticallydeformed, the leg 40 is less likely to be worn or deteriorated early,and the increase in an operation resistance of the orbital sander 10does not occur. Therefore, the life of the leg 40 is prolonged ascompared with the conventional art, and only periodical greasing(lubrication) to the first recess and protrusion engagement portion 50and the second recess and protrusion engagement portion 60 is requiredfor maintenance of the orbital sander 10. Further, since the leg 40 ismade of rubber, operating noise of the orbital sander 10 can be reducedwhile absorbing size errors of parts forming the orbital sander 10.However, when it is possible to form the parts with the precision withwhich almost no size error occurs, the leg 40 may be made of, forexample, hard plastic or aluminum (high hardness member) instead ofrubber.

As described in detail above, according to the orbital sander 10 of thefirst embodiment, the first recess and protrusion engagement portion 50and the second recess and protrusion engagement portion 60, which makethe fan guide 23 and the one end portion 40 a of the leg 40 swingablyabut on each other and make the base plate 31 and the other end portion40 b of the leg 40 swingably abut on each other, and restrict thedeviation of the leg 40 relative to the fan guide 23 and the base plate31 in the horizontal direction while allowing the swinging of the leg 40relative to the fan guide 23 and the base plate 31, are provided betweenthe fan guide 23 and the one end portion 40 a and between the base plate31 and the other end portion 40b, respectively. As a result, the leg 40can swing with almost no resistance without involving any elasticdeformation during the orbital motion of the base 30. Accordingly, sincethe stress (load) to cause the elastic deformation is not applied to theleg 40 unlike the conventional art, the increase in operation resistanceof the base 30 can be prevented and the life of the leg 40 can beprolonged to extend the maintenance cycle.

Also, according to the orbital sander 10 of the first embodiment, thefirst recess and protrusion engagement portion 50 and the second recessand protrusion engagement portion 60 are composed of the sphericalprotrusion portions 51 a and 61 a provided on the fan guide 23 and thebase plate 31, respectively, and the spherical recess portions 52 and 62provided on the one end portion 40 a and the other end portion 40b,respectively. Further, the radii R1 of the spherical protrusion portions51 a and 61 a are set to be smaller than the radii R2 of the sphericalrecess portions 52 and 62 (R1<R2). Therefore, the fan guide 23 and theleg 40 can be brought into point contact with each other and the baseplate 31 and the leg 40 can be brought into point contact with eachother, so that the leg can be swung smoothly.

Next, a second embodiment of the present invention will be described indetail with reference to the drawings. Incidentally, portions having thesame functions as those of the above-described first embodiment aredenoted by the same reference numerals and detail descriptions thereofare omitted. FIG. 5 is a partial sectional view showing a leg and asurrounding structure thereof according to the second embodiment andcorresponding to FIG. 3.

As shown in FIG. 5, an orbital sander (power tool) 70 according to thesecond embodiment is different from the orbital sander 10 according tothe first embodiment in a leg and a surrounding structure thereof.Specifically, a first recess and protrusion engagement portion (recessand protrusion engagement portion) 80 of the orbital sander 70 iscomposed of a steel ball 81 having a radius R3 and a spherical recessportion 82 having a radius R3 and provided at one end portion 100 a of aleg (post) 100. Also, a second recess and protrusion engagement portion(recess and protrusion engagement portion) 90 of the orbital sander 70is composed of a steel ball 91 having a radius R3 and a spherical recessportion 92 having a radius R3 and provided at the other end portion 100b of the leg 100.

Here, the respective steel balls 81 and 91 constitute sphericalprotrusion portions in the present invention, and the respective steelballs 81 and 91 are attached to an engagement recess portion 71 b formedin a base-side surface 71 a of a fan guide (main body part) 71 and anengagement recess portion 72 b formed in a fan-guide-side surface 72 aof a base plate 72, respectively. Approximately halves of the respectivesteel balls 81 and 91 protrude toward the leg 100, respectively, andthey enter the respective spherical recess portions 82 and 92 of the leg100 to come in sliding contact with them. Incidentally, depths of therespective spherical recess portions 82 and 92 are set to be smallerthan the radii R3 of the respective steel balls 81 and 91. In thismanner, in the swinging action of the leg 100, the contact between theone end portion 100 a and the base-side surface 71 a and the contactbetween the other end portion 100 b and the fan-guide-side surface 72 aare prevented.

In the first recess and protrusion engagement portion 80 and the secondrecess and protrusion engagement portion 90, unlike the firstembodiment, the leg 100 and the respective steel balls 81 and 91 aremade to swingably abut on (come in sliding contact with) each otherthrough spherical surfaces having the same radius R3. Therefore,rattling of the leg 100 can be further suppressed as compared with thefirst embodiment. However, it is desired that sufficient grease isapplied to the sliding contact portions in order to prevent the abrasionof the leg 100 and realize the smooth orbital motion of the base 30.

The orbital sander 70 according to the second embodiment is providedwith an annular first surrounding wall 71 c with a height h3 protrudingfrom the base-side surface 71 a of the fan guide 71, and further anannular second surrounding wall 72 c with a height h4 protruding fromthe fan-guide-side surface 72 a of the base plate 72 (h4<h3). However,the heights h3 and h4 of the first surrounding wall 71 c and the secondsurrounding wall 72 c can be arbitrarily set like the first embodiment(see FIG. 3).

Annular gaps G1 which are larger than those in the first embodiment areformed between the first and second surrounding walls 71 c and 72 c andthe leg 100. As a result, even if the inclination angle of the leg 100reaches the maximum inclination angle α° in the swinging action of theleg 100, the contact between the first and second surrounding walls 71 cand 72 c and the leg 100 can be prevented. Therefore, the taper surfaceson the radially inner sides of the first surrounding wall and the secondsurrounding wall provided in the first embodiment are not provided.

As described in detail above, also in the orbital sander 70 according tothe second embodiment, the function effects similar to those in thefirst embodiment can be achieved except for the function effect obtainedby “point contact” in the above-described first embodiment. In addition,since the respective steel balls 81 and 91 are used in the first recessand protrusion engagement portion 80 and the second recess andprotrusion engagement portion 90 in the second embodiment, costreduction of the orbital sander 70 can be realized by adoptinggeneral-purpose steel balls defined in JIS or the like as the respectivesteel balls 81 and 91.

Next, a third embodiment of the present invention will be described indetail with reference to the drawings. Incidentally, portions having thesame functions as those of the above-described first embodiment aredenoted by the same reference numerals and detail descriptions thereofare omitted. FIG. 6 is a partial sectional view showing a leg and asurrounding structure thereof according to the third embodiment andcorresponding to FIG. 3.

As shown in FIG. 6, an orbital sander (power tool) 110 according to thethird embodiment is different from that according to the firstembodiment in a leg and a surrounding structure thereof. Specifically,the relationship of recess and protrusion in a first recess andprotrusion engagement portion (recess and protrusion engagement portion)120 and a second recess and protrusion engagement portion (recess andprotrusion engagement portion) 130 is inverted to that in the firstembodiment. In other words, spherical protrusion portions 121 and 131having a radius R4 are integrally provided to one end portion 140 a andthe other end portion 140 b of a leg (post) 140 so as to protrude towarda fan guide (main body part) 111 and a base plate 112. Here, in thethird embodiment, the leg 140 is made of aluminum.

A spherical recess portion 122 with a radius R4 which the sphericalprotrusion portion 121 enters and comes in sliding contact with isprovided on a base-side surface 111 a of the fan guide 111. Here, thespherical protrusion portion 121 and the spherical recess portion 122form the first recess and protrusion engagement portion 120. On theother hand, a flexible rubber seat 113 is placed on a fan-guide-sidesurface 112 a of the base plate 112, and a spherical recess portion 132with a radius R4 which the spherical protrusion portion 131 enters andcomes in sliding contact with is provided on a fan-guide-side surface113 a of the rubber seat 113. Here, the spherical protrusion portion 131and the spherical recess portion 132 form the second recess andprotrusion engagement portion 130. Incidentally, when it is possible toform the parts with the precision with which almost no size erroroccurs, it is possible to adopt the configuration in which the rubberseat 113 is eliminated and a spherical recess portion is formed in thebase plate 112 so that the spherical protrusion portion 131 enters thespherical recess portion to be brought into sliding contact with thesame.

Here, the contact between the one end portion 140 a of the leg 140 andthe base-side surface 111 a and the contact between the other endportion 140 b of the leg 140 and the fan-guide-side surface 113 a of therubber seat 113 are prevented in the swinging action of the leg 140. Inthe first recess and protrusion engagement portion 120 and the secondrecess and protrusion engagement portion 130, since the leg 140 and thespherical recess portions 122 and 132 are made to swingably abut on(brought into sliding contact with) each other through sphericalsurfaces having the same radius R4, rattling of the leg 140 can befurther suppressed like the second embodiment. However, it is desiredthat sufficient grease is applied to the sliding contact portions inorder to prevent the abrasion of the rubber seat 113 and the fan guide111 and realize the smooth orbital motion of the base 30.

The orbital sander 110 according to the third embodiment is providedwith an annular first surrounding wall 111 b with a height h5 protrudingfrom the base-side surface 111 a of the fan guide 111. Further, anannular second surrounding wall 112 b with a height h6 is provided onthe base plate 112 of the orbital sander 110 so as to protrude from thefan-guide-side surface 113 a of the rubber seat 113 (h6<h5). However,the heights h5 and h6 of the first surrounding wall 111 b and the secondsurrounding wall 112 b can be arbitrarily set like the first embodiment(see FIG. 3).

Annular gaps G2 larger than those in the first embodiment are formedbetween the first and second surrounding walls 111 b and 112 b and theleg 140 like the second embodiment. Therefore, even if the inclinationangle of the leg 140 reaches the maximum inclination angle α° along withthe swinging action of the leg 140, the contact between the first andsecond surrounding walls 111 b and 112 b and the leg 140 can beprevented. Accordingly, also in the third embodiment, taper surfaces onthe radially inner sides of the first surrounding wall and the secondsurrounding wall are not provided like the second embodiment.

As described in detail above, also in the orbital sander 110 accordingto the third embodiment, the function effects similar to those in thefirst embodiment can be achieved except for the function effect obtainedby “point contact” in the above-described first embodiment.

Next, a fourth embodiment of the present invention will be described indetail with reference to the drawings. Incidentally, portions having thesame functions as those of the above-described first embodiment aredenoted by the same reference numerals and detail descriptions thereofare omitted. FIG. 7 is a partial sectional view showing a leg and asurrounding structure thereof according to the fourth embodiment andcorresponding to FIG. 3.

As shown in FIG. 7, an orbital sander (power tool) 150 according to thefourth embodiment is different from that according to the firstembodiment in a leg and a surrounding structure thereof. Specifically, afirst recess and protrusion engagement portion (recess and protrusionengagement portion) 160 of the orbital sander 150 is composed of aconical protrusion portion 161 with an angle of β° provided on a fanguide (main body part) 151 and a conical recess portion 162 with anangle of γ° provided at one end portion 170 a of a leg (post) 170(γ°>β°) Further, a second recess and protrusion engagement portion(recess and protrusion engagement portion) 180 of the orbital sander 150is composed of a conical protrusion portion 181 with an angle of β°provided on a base plate 152 and a conical recess portion 182 with anangle of γ° provided at the other end portion 170 b of the leg 170.

A height of the conical protrusion portion 161 from a base-side surface151 a of the fan guide 151 is set to be larger than a depth of theconical recess portion 162 from one end portion 170 a of the leg 170.Further, a height of the conical protrusion portion 181 from afan-guide-side surface 152 a of the base plate 152 is set to be largerthan a depth of the conical recess portion 182 from the other endportion 170 b of the leg 170. In this manner, in the swinging action ofthe leg 170, the contact between the one end portion 170 a and thebase-side surface 151 a and the contact between the other end portion170 b and the fan-guide-side surface 152 a are prevented.

However, the leg 170 is not limited to that made of rubber and it maybemade of hard plastic or aluminum with hardness higher than that ofrubber. In this case, in order to reduce operating noise due to theswinging action of the leg 170, a rubber seat may be disposed on thebase plate 152 like the orbital sander 110 (see FIG. 6) of the thirdembodiment. In this case, the conical protrusion portion may be providedintegrally on the rubber seat or a conical protrusion portion made ofaluminum may be placed on the rubber seat.

As described in detail above, also in the orbital sander 150 accordingto the fourth embodiment, since distal end portions of the conicalprotrusion portions 161 and 181 are brought into almost point contactwith bottom portions of the conical recess portions 162 and 182,function effects similar to those of the above-described firstembodiment can be achieved.

It goes without saying that the present invention is not limited to therespective embodiments described above and various modifications andalterations can be made within the gist of the present invention. In therespective embodiments described above, structures where the firstsurrounding walls 23 b, 71 c and 111 b are provided on the fan guides23, 71, 111, and 151 and the second surrounding walls 31 b, 72 c and 112b are provided on the base plates 31, 72, 112, and 152 have been shown,but the present invention is not limited to these. For example, if it ispossible to increase the hardness of the legs, the legs do notelastically deform and do not fly out of the respective surroundingwalls, and the respective surrounding walls can be eliminated. In thiscase, the structures of the fan guide and the base plate can besimplified and the manufacturing cost of the orbital sander can bereduced.

What is claimed is:
 1. A power tool comprising: a main body part havinga driving source; a rotation shaft provided in the driving source; abasemoving in an approximately circular motion with respect to the main bodypart in a horizontal direction along with rotation of the rotationshaft; a polishing sheet held by the base; a post provided between themain body part and the base; and recess and protrusion engagementportions provided between the main body part and one end portion of thepost and between the base and the other end portion of the post,respectively, making the main body part and the one end portionswingably abut on each other and making the base and the other endportion swingably abut on each other, respectively, and restricting adeviation of the post relative to the main body part and the base in ahorizontal direction while allowing swinging of the post relative to themain body part and the base.
 2. The power tool according to claim 1,wherein the recess and protrusion engagement portions are composed ofspherical protrusion portions or spherical recess portions provided onthe main body part and the base, respectively, and spherical recessportions or spherical protrusion portions provided on the one endportion and the other end portion, respectively.
 3. The power toolaccording to claim 2, wherein radii of the spherical protrusion portionsare set to be smaller than radii of the spherical recess portions.